A. Field of the Invention
This invention relates to cured fibers and more particularly relates to a process for the manufacture of a fiber containing at least 85% by weight of a cross-linked novolac i.e. novoloid, and the fiber resulting from the process.
B. History of the Prior Art
In the prior art phenolic resin fibers were manufactured by fiberizing uncured phenolic resins. The uncured fibers were then cured by heating them in an environment containing a cross-linking agent and a catalyst.
This method of manufacturing phenolic resin fibers is undesirable since the process time is extensive, generally running from 6 to 16 hours from the time the process begins until the cured phenolic resin fiber is obtained.
In addition, manufacturing phenolic resin fibers by this method, even after extended curing time, frequently does not result in a completely cured fiber since cure of the inside of the fiber is dependent upon diffusion of cross-linking agent and catalyst through the exterior of the fiber.
It is most desirable to manufacture phenolic resin fibers beginning with novolac phenolic resins, i.e. those phenolic resins manufactured from phenol and formaldehyde wherein excess phenol is used. The novolac resins are preferred due to their ease of manufacture and control and in addition, it is somewhat easier to cure novolac resins in the fiber form. Furthermore, it is easier to control the extent of curing and cross-linking of novolac in fiber form than the curing of other types of phenolic resins in fiber form. In particular, the resols, i.e. those phenol-formaldehyde resins wherein excess formaldehyde is used, are most difficult to control during manufacture and are more difficult to cure and control when fibers are being formed. Furthermore, it is more difficult to obtain thermoplastic resols which can be subsequently melted to form fibers.
In the prior art attempts to obtain novoloid fibers by fiberizing a melted blend of a novolac resin and a cross-linking agent were unsuccessful since curing occurred which interferred with the fiberizing process.